How do I get the bounding box of all objects in a scene
Bounding box coords of all meshes in scene.
Pretty sure this has been answered before, but finding it is another matter.
Here is some numpy code I use to create a bounding box for all mesh objects in a scene
Basically, list coordinates of all bounding box coordinates of all mesh objects in the scene.
Use the  minima / maxima of each axis produce an axis aligned bounding box encompassing all others.
import bpy
from mathutils import Vector
from bpy import context
import numpy as np
import itertools

# multiply 3d coord list by matrix
def np_matmul_coords(coords, matrix, space=None):
    M = (space @ matrix @ space.inverted()
         if space else matrix).transposed()
    ones = np.ones((coords.shape[0], 1))
    coords4d = np.hstack((coords, ones))
    
    return np.dot(coords4d, M)[:,:-1]
    return coords4d[:,:-1]

# get the global coordinates of all object bounding box corners    
coords = np.vstack(
    tuple(np_matmul_coords(np.array(o.bound_box), o.matrix_world.copy())
         for o in  
            context.scene.objects
            if o.type == 'MESH'
            )
        )
print(&quot;#&quot; * 72)
# bottom front left (all the mins)
bfl = coords.min(axis=0)
# top back right
tbr = coords.max(axis=0)
G  = np.array((bfl, tbr)).T
# bound box coords ie the 8 combinations of bfl tbr.
bbc = [i for i in itertools.product(*G)]
print(np.array(bbc))